Human Functional Anatomy 213 the Upper Limb Early Limb Development

HUMAN FUNCTIONAL ANATOMY 213 THE UPPER LIMB EARLY LIMB DEVELOPMENT

THIS WEEKS LAB: IN THE FISH (or early human embryo) Proximal parts, plexuses and patterns Slight elevations of ectoderm appear in lateral plate (4th week). Apical ectodermal ridge induces proliferation of limb mesenchyme. READINGS Dorsal and ventral muscle masses connect the girdle to the limb bud. Stern. Essentials of Gross anatomy – The upper limb Limb girdle in body wall Stern. Core concepts in Anatomy:- 80: Organization of upper limb musculature and the Proximal, middle and distal segments of the limb brachial plexus Faiz and Moffat. Anatomy at a Glance:- Nerves of the Upper limb 1 & 2 (parts 30 &31) Grant's Method:- Upper limb and Back (especially pectoral region and axilla) OR any other regional textbook - similar sections

IN THIS LECTURE I WILL COVER: Ontogeny and Phylogeny The Pectoral fin The primitive tetrapod forelimb Rotations of the limb in phylogeny Dorsal and ventral muscle/nerve/girdle bone Segmental nerve supply and muscle groups Brachial plexus Muscle groups of the upper limb The fin, or paddle has: Preaxial and postaxial borders (front and back edges) Dorsal and ventral surfaces (top and bottom) Dorsal muscles elevate the fin. Attach to dorsal elements of the girdle (“scapula” and vertebrae) Ventral muscles depress the fin. Attach to ventral elements of the girdle (coracoid)

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PRIMITIVE TETRAPOD FORELIMB MAMMALIAN FORELIMB ROTATIONS 90 degrees LATERAL ROTATION The characteristic segments of the limb (shoulder, arm, forearm, & hand) Were present in the fins of fossil fish The preaxial border (thumb side) becomes dorsal But became fully developed in terrestrial forms (amphibia & reptiles) This brings the dorsal muscles to the posterior aspect of the limb and the ventral muscles to the anterior aspect

The orientation of the limb is still the same: Dorsal is dorsal and Ventral is ventral Pre-axial (thumb side) is front edge of limb

The limbs and mode of locomotion are very similar in fish & reptiles 5 6

MAMMALIAN FORELIMB ROTATIONS DORSAL AND VENTRAL MUSCLES 90 degrees ADDUCTION The limb rotations modify the action of the muscles Adduction brings the limb under the trunk. (Classic mammalian posture) Primitive dorsal elevators and ventral depressors of the fin Preaxial border (thumb side) becomes lateral Become dorsal extensors, and ventral flexors of the limb Dorsal muscles remain on the posterior aspect of the limb Dorsal muscles either: Attach to the vertebral column or the true scapula or Lie in dorsal compartments of the limb

Ventral muscles either: Attach to the coracoid part of the scapula, clavicle, ribs or sternum or Lie in ventral compartments of the limb

Quadrupedal animals pronate their forearm so that the digits face forwards

In humans the limb stays in the same orientation, but we stand on our hindlimbs and the upper limb hangs at our side (90 degrees extension)

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Dorsal and Ventral BRACHIAL PLEXUS MUSCLE COMPARTMENTS OF THE UPPER LIMB TRUE LIMB MUSCLES ATTACH TO LONG BONES OF THE LIMB And their Dorsal and Ventral nerves The brachial plexus supplies all these muscles. This excludes muscles attaching the axial skeleton to the scapula. Ventral: These muscles are derived from cranial or cervical myotomes Musculocutaneous nerve (C56) Eg. Trapezius and sternomastoid - Accessory nerve CN 11 Anterior compartment of the arm Serratus anterior, rhomboids, levator scapulae - C3,4,5,6

Dorsal: C5 C6 C7 C8 T1 Radial nerve (C5678T1) ROOTS Posterior compartment of the arm

TRUNKS Upper Middle Lower Ventral: Median nerve C5678T1 Anterior compartment of the forearm DIVISIONS Anterior and posterior for each trunk

Dorsal: Radial nerve (C5678T1) CORDS Lateral Posterior Medial Posterior compartment of the forearm

Ventral: NERVES Musculocutaneous Median Ulnar Ulnar nerve (C8T1) Hand Axillary Radial

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BRACHIAL PLEXUS MUSCLE COMPARTMENTS OF THE UPPER LIMB Basis of the brachial plexus

Compartment Segments Nerve Anterior shoulder C5 & C6 Pectoral nerves Ventral

Posterior shoulder C5 & C6 Axillary Dorsal Suprascapular Subscapular & thoracodorsal

Anterior arm C6 & Musculocutaneous Ventral

Posterior arm C6 & Radial nerve Dorsal

Posterior forearm C7 & Radial nerve Ventral

Anterior forearm C7 & Median (and ulnar) nerves Ventral

Hand C8 & T1 Ulnar (and median) nerve Ventral

The brachial plexus is how the nerves of the upper limb are formed. You can see the need for a plexus, otherwise there would be a mess of tiny nerves.

“ONTOGENY RECAPITULATES PHYLOGENY” Ernst Haeckel

Ontogeny = The development of the individual Phylogeny = Evolution of the species

The development of the individual recapitulates the evolution of the species

Classic example is the Development of the frog. Retracing the evolution of vertebrates from fish to reptiles

From the tadpole stage (like a fish)

1. Water breathing creature with tail and no limbs 2. Rudimentary limbs 3. Reduction of tail 4. Breathes air 5. Fully developed limbs,, loss of tail, becomes a land animal.

To the fully developed frog

I WANT TO TRACE THE DEVELOPMENT OF THE LIMBS IN VERTEBRATES AND COMPARE IT TO THE GROWTH OF LIMBS IN THE INDIVIDUAL